These studies deal with (a) the neuroendocrine basis of seasonal anestrus in the ewe and (b) localization and pharmacological characterization of the hypothalamo-hypophyseal centers involved in E- induced LH release in the ewe. Studies in the anestrous ewe are comparing levels of LH and FSH in serum and anterior pituitary glands, and levels of gonadotropin releasing hormone and FSH and LH releasing hormone activities in the hypothalamus and pineal glands of anestrous and cyclic ewes. The effect of surgical deafferentation of the hypothalamus on gonadotropin levels and sexual behavior of anestrous ewes is being determined. The type of neural pathways involved in LH release is being determined by studying the effects of neural blocking drugs such as reserpine, phentolamine, and phenoxybenzamine on basal LH levels and on estrogen-induced LH release in ovariectomized ewes. Other studies are examining the effect of frontal and total hypothalamic deafferentation on basal LH levels and on estrogen-induced LH release in ovariectomized ewes.